1. Field of the Invention
The invention relates to a piston rod-less pneumatic cylinder, with a piston longitudinally movable inside a cylinder tube and a transmission element that engages with this piston and projects out through a longitudinal slot in the cylinder tube, along with a sealing tape that seals the longitudinal slot from the inside on either side of the piston, which is routed through the piston in the area of the transmission element, and exhibits a sealing strip that interacts with two longitudinally extending sealing areas near the end of the longitudinal slot inside the cylinder, along with at least one fixing strip arranged on the outside of the sealing strip with two fixing elements that lie opposite one another relative to the center plane of the longitudinal slot, and are essentially longitudinally extended and directed toward the outside, and with an outer band that at least partially covers the longitudinal slot from outside on either side of the piston, wherein this outer band exhibits fixing elements that engage the fixing elements of the sealing tape to secure the sealing tape in the longitudinal slot, with the sealing tape being spaced apart from the walls of the longitudinal slot except for the sealing areas.
2. The Prior Art
Piston rod-less pneumatic cylinders vary widely in design, and are most often used as pneumatically actuated working cylinders in arrangements where the smaller fitting length is advantageous relative to cylinders with piston rods. The force exerted on the piston by the pressure medium is conveyed from the transmission element that projects out through the lateral longitudinal slot to the device to be operated. The delivery chambers lying on either side of the piston are sealed off by packing rings or sealing cuffs on the piston, and also by the sealing tape abutting from the inside on the longitudinally extended sealing areas near the end of the longitudinal slot, wherein the sealing tape is routed through in the inside under the transmission element of the piston in the unpressurized area between the piston seals.
The sealing tape is pressed against the longitudinally extended sealing areas by the pressure prevailing in the respectively pressurized cylinder interior. However, precautions must normally be introduced to prevent the sealing tape from sagging into the interior when the latter is in an unpressurized state, since this would result in at least a temporary leak as pressure begins to build in this previously unpressurized interior.
In the above connection, for example, EP 69 199 B1 discloses a pneumatic cylinder of the kind mentioned at the outset in which an outer band that covers the longitudinal slot from outside to prevent foreign objects, contaminants and the like from penetrating is provided simultaneously to hold the inner sealing tape. To this end, the fixing strip located centrally in the sealing strip or sealing tape exhibits projections on both sides as longitudinally extended fixing elements that are overlapped by two accompanying ledge-shaped fixing elements of the outer band. As a result, the sealing tape is held with an overall positive fit to the outer band, and hence in the longitudinal slot, even if no pressure is acting on the sealing tape from the inside. Since the longitudinal slot itself can remain free of fixing grooves and the like, the cylinder tube is relatively simple in design, wherein the transmission element can also be laterally guided or supported in the longitudinal slot.
The only disadvantage to the discussed known design is the fact that engaging and disengaging the sealing tape mount on the outer band does require relatively high forces due to the joint with a positive fit, which must be taken into account in the structure and design of the interacting bands, in particular to prevent the outer band from becoming drawn into the longitudinal slot or lifting off of the longitudinal slot due to the inner sealing tape. The object of this invention is to avoid the mentioned disadvantages, in particular to improve a pneumatic cylinder of the kind mentioned at the outset in such a way as to simplify the securing of the sealing tape during the safe operation of the arrangement.